1776 - Bushnell's Submersible Craft

David Bushnell, 36 years old, a medical student, together with renowned Inventor and Mechanic Isaac Doolittle, 55 years old, and with Phineas Pratt, a carpenter, built last year a strange gear, nicknamed and finally named Turtle owing to its shape and to its look when immersed in water.

Benjamin Gale in a letter

Its acknowledged purpose is warfare, that is attaching then blowing up a mine under the hulls of moored British vessels which are blockading the insurgent colonies. In this project, Bushnell received much help from influential Benjamin Gale, a physician and a politician, 66 years old, to fund it and to link with insurgent political circles. His goal has been achieved : Turtle has just been trialed at war.

¤ David Bushnell started his medical studies four years ago after a first life as a farmer. He sinks in a wide spectrum of topics and demonstrates much ingenuity. He has co-invented a system to trigger an underwater mine that he has just developed in the form of an underwater time bomb. He thought about a submersible gear once he realised he had a weapon without having a vehicle for it. He may have heard of the prototype designed and built by Cornelis Drebbel a hundred fifty years ago.

¤ Between 1620 and 1624, Drebbel, an artist and an inventor, 48 years old in 1620, built in succession three so-called diving boats, and trialed them on and beneath the surface of the Thames river. The first boat was described by a contemporary diarist as being able of navigating between two waters over a few miles, between Westminster and Greenwich - a 7-mile trip. Nothing is known of its intended purpose, or of its structure, or of the way it navigated either. We just know that, 1st, the crew could breath air through an intake pipe owing its buoyancy to a few floats, 2nd, the boat could dive and surface through a ballast and a pump, 3rd, it moved through oars. Watertightness owed to layers of leather and to grease.

The craft is 7-foot long - some witnesses say nine or ten -, 3-foot broad and 5-foot deep.

¤ Its gross volume is likely something between 3½ and 4 tons. Assuming a 90% buoyancy, we get a displacement around 3½ to 4 tons, including some 200-pound of brains and muscles, some 700-pound operative ballast to immerse the craft, and some 300-pound emergency ballast to restore buoyancy. The values mentioned here and there are so low that they do not make sense.

It is meant to being operated by a single man, who, taking into account job difficulty, could be described as a one-man-band as well as a strong drudge. He is supposed to steer and to move the paddles through a hand-driven crankshaft to reach the enemy ship - the paddles are one-foot long, which raise doubts on the possibility of moving such a heavy craft at two and a half knots, as it has been said. He has also to act upon buoyancy through the foot-driven ballast pump and a hand-driven vertical propeller. Once the target reached, he is supposed to maintain the craft stationary along it and to drill the hull, then to attach the mine and to trigger the time bomb before escaping - all that gruelling work within a 30-minute autonomy between two air intakes.

Curiously there were volunteers for this quasi suicide mission. The winner was Ezra Lee, 27 years old. He did it twice and failed twice despite his gallantry and his stubborn tenacity. His first attempt aimed at 64-gun Eagle moored in front of New York. He struggled currents for two hours at night before reaching the target. There he did two unsuccesful attempts, before delivering the mine which exploded in the stream of East river. His second attempt aimed at a frigate harboured at Manhattan. He was spotted by the watch and gave up.

¤ Lee's prowess is so extraordinary that it is not believed in Britain. At best, they believe that an attack by a floating mine took place. There is no record of an attack on the British side.

Turtle sunk four days later in Hudson river aboard the sloop which was its tender.

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IN RETROSPECT FROM TODAY

Note - about Bushnell

He does not rebuild another Turtle. He builds a number of floating mines, that he names torpedoes, that he uses against the ships moored on Delaware river blockading Philadelphia. He only sinks a schooner that way. His sponsors are frustrated so Lee stops producing mines and joins the Continental army. He falls into obscurity after the war. After a passage in France, he comes back, changes his name and practices medicine.

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SUGGESTED BIBLIOGRAPHY

Dictionary of American Naval Fighting ships - Turtle I (Submarine) - 2010 - available on the internet